Lamp filament



Aug. 27, 1929. P m 1,726,365

LAMP FILAMENT Filed May 10, 1928 Fig.1. Fig. 2. Fig 3. Fig.4.

Inventor; Marcello Pirani,

His Attoflfiegf STATES PATENT QFFIQE.

MARCELLO PIRANI, OF BERLIN-WILMERSDORF, GERMANY, .ASSIGNOR TO GENERAL ELECTRIC 'COMPANY, A CORPORATION OF NEW YORK.

LAMP FILAMENT.

Application filed May 10, 1928, Serial No. 276,791, and. in Germany- .Tuly 13, 1927.

My invention relates to incandescent lamps and more particularly to such lamps in which the filament is made of a flat metal band or ribbon bent into a serpentine shape with straight flat sections side by side and parallel. i

The principal object of the invention is to provide a filament so shaped that it acts much like a flat surface of uniform bril- 1o liance and is particularly useful as alight source in projection apparatus where the field of illumination on the screen should be as nearly uniform as possible. To this end and in accordance with the invention the metal sheet of which the filament is made is folded or bent to produce two groups or parallel rows of straight ribbons or flat sec tions, each row comprising several straight sections placed in the same plane edge to edge and separated by slots, the two rows being staggered or displaced so that the straight sections in one row overlap the slots between sections in the other row. The intermediate portions between the straight sections are bent in such a way as to position the two groups of straight sections in parallel planes so disposed that these sections complement one another and cooperate to produce a solid light surface when viewed along the direction of rejection. The sheet is cut into sections y parallel slots extending nearly across the sheet alternately from opposite sides, and by folding the sheet so that the slots between the parallel straight flat sections of one group are overlapped by the straight sections of the other group the slots between sections almost or entirely disappear when viewed along a' line normal to the fiat sections, and the filament is concentrated into a small space. There is thus ob tained by this invention a substantially uniform lighting surface of great brilliance which is of advantage in many cases, particularly for projection purposes.

My invention will best be understood.in connection with the accompanying drawings, in which Figs. 1 and 2 show, in plan View and in section, a blank from which a sinuous or serpentine fiat strip filament may be made; Figures 3 and 4 show in front view and in section one example of the serpentine flat strip filament; Figure 5, shows the same filament in perspective; Figures 6 blank for a flat strip filament with somewhat and 7 show in plan view and in section awider spacing between sections; Figure 8 shows that filament in perspective, and F1gure 9 is an elevation of an electric incandescent lamp equipped with the new filament. I 30 In the production of the new filament shown in Figures 3 to 5, the first step is the making of the sinuous filament blank, shown in Figures 1 and 2, which is produeed from a fiat metal sheet in the usual way by punching to leave flat sections a separated by the slots 6 which extend nearly across the sheet and alternately from opposite sides, leaving the section connected at their ends by the intermediate portions or bridges c. In this filament blank all the parallel sections a separated by the slots Z) lie side by side in one plane.

This filament blank is folded at the bridges or junctions 0 between adjoining sections a to obtain the filament shaped as shown in Figures 3 t0 5, the junctions or bridges 0 being bent along their center lines d-d somewhat more than 90 degrees to bring the flat sections a of the blank place as the flat sections a, a of the shaped filament, and to form between these sections deep grooves or troughs 6 having for their sides the intermediate and backwardly bent fiat sections a a, and for their bottoms the flat sections a, a This folding, which gives the filament a zigzag shape in cross section, as shown in Fig. 4, causes the slots 5 between adjacent flat sections to disappear from view when the filament is viewed along a line normal to the sections a, a in the direction of the arrow in Figure 4:, which is the projection axis or direction of the principal radiation of the filament. The flat sections of the filament are so disposed as to overlap 95 and form a concentrated and apparently continuous and homogenous light emitting surface of very great brilliance when viewed from a point on the projection axis.

The production of the filament shown in 100 Figures 7 and 8 is started with the sinuous or serpentine-shaped blank shown in Figure 6, which has somewhat wider slots 6 between the flat sections and consequently longer bridges or intermediate sections 0. The 105 bridges are bent back to their full extent by folding along the lines ;f and g, which align with the edges 0 the sections a. All flat sections of the filament then lie alternately in two relatively parallel planes, since no that flat section intermediate the two flat sections in oneplane is in the other and parallel plane. The lateral dimensions and depth of the troughs e are in this case determined only by the length and inclination or the form of the bridges 0. In this form of filament the spaces or slots b between the flat sections are overlapped by the flat sections win the direction of the principal radiation and in this case also there is produced by the folding of the filament blank a small but apparently continuous and uniform light emitting surface of great brilliance.

The two ends of the new filament can be fastened in anydesired manner to the leads which supply the current. i Figurel) shows one example of how filaments a fastened to leads 7L may easily be centrally located in a lamp bulb is by meansof a stem VVhat I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric incandescent projection lamp a filament comprising straight flat strips placed edge to edge and in the same plane substantially normal to the projection axis with slots narrower than said strips between their edges, and similar strips similarly placed in a parallel plane to overlap the slots between the edges of the strips in the first plane whereby the strips in the two planes complement one another and produce the effect of a continuous light emitting surface which is normal to the projection axis.

2. In an electric incandescent projection .to edge in two parallel planes normal to the projection axis with each section inone plane overlapping the slot between the edges of adjacent sections in the other plane, the sections intermediate those in said two planes being approximately parallel to the projection axis and forming the sides of troughs of which the sections in said two planes are i the bottoms whereby all sections in the aggregate produce the effect of a continuous light emitting surface.

3. In an electric incandescent projection lamp a filament formed of a sinuous strlp of metal with a plurality of straight parallel sections joined at alternate ends by intermediate portions bent to extend at approximately right angles to said straight sections to space said straight sections apart with alternate sections lying in parallel planes but staggered to cause the edges of each two adjacent sections in one plane to be overlapped by the intermediate and parallel section in the other plane and thereby produce the effect of a continuous surface when viewed along the projection axis normal to said planes.

In witness whereof I have hereunto set my hand this 25th day of April, 1928.

l /LARCELLO PIRANI. 

